presentation no 1 (1) (1)

8/10/2019 Presentation No 1 (1) (1)

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Topic: Sorption isothermand

food preservation

Introduction to Food science and technology class

Submitted to Dr. Nguyen Vu Hong Ha


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Outline of contents

Water Properties, MicelleWater activity

Water sorption isotherm

Hysteresis

Food Microbiology growth

Food preservation methods


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Properties of water

Heat capacity of water

Hydrogen bonds

Dipole

Oxygen has high electronegativity

Water can be a solvent


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Dispersing action

Mixing without solvation >> dispersion.

Eg of dispersion:

Water interact with amphiphilic molecule >>micelles

Eg of micelles:

Vitamin A, D Milk


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Micelle

Water interact hydrophilic heads

Hydrophobic tail hidden away


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Moisture is the amount of water

present in food. It usually take 3 forms:

Free water

Adsorbed water

Bound water


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Free water

Water that is no boundwith the other

subtance.

Its lightly entrapped

and therefore easilyseparated from

foods,similar properties

like pure water.


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Adsorbed water

This water associates in lay-ers via intermolecular

hydrogen bonds around hydrophilic food

molecules.


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Bound water

Water that is bound to different molecules

such as proteins and carbohydrates.

It exists in a tight chemically bound situation.


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Water acivity

Water activity (aw)isexpressed as the ratio

of the vapour

pressure in food (P)

to the vapourpressure of purewater (PO)at the same

temperature:

aw= P/PO


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Water sorption isotherms( or MSI)

The relationship between water activity and

moisture content at a given temperature


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Water sorption Isotherm


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Water activity and its influence

Water activity changes with temperature thus it is necessary to

control remperature.

Purposes for controling temperature:

- aw- measurement at a defined temperature

- Lab to lab sample comparison- Isotherm determination


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Temperature and water activity

Water binding

Dissociation of water

Solubility of solutes in water State of the matrix (glossy or rubbery)


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Some substances have increased water activity

with increasing temperature, while others show

a decrease with increasing temperature.Depends on how

temperature affects the

factors that control water

activity in the substance.


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Hysteresis

Capillary condensation theory

The pore adsorbed by vapor

Vapor is taken out from the pore. The difference between adsorption and

desorption is hysteresis


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Effects of water removed

When too much water is desorbed

Water is taken out from the Bound water


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Adsorption and Desorption

Foods will equilibrate to a point of equilibrium

with its environment

Desorption is when a wet food is placed in a

dry environment

Adsorption is when a dry food is placed in a

wet environment (lumping, clumping)


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Effects of Temperature

Hysteresis size decreases as temperature

increases

Increased temperature increase diffusion in

and out

Help the system move toward the equilibrium


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Influence of the water activity on the

productWater activity is responsible for the growth of undesirable organisms

like bacteria or fugi which produce toxins or other harmful subtances.

The following properties of a product are effected:

Microbiological stability

Chemical stability

Content of proteins and vitamins

Color, taste and nutrional value

Stability and durability

Solubility and texture


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Factor that influence water activity:

Drying: water activity is decreased byphysically removing water

Solutes: water activity is decreased by adding

solutes such as salt or sugar Freezing: water activity is decreased by

feezing

Combination: one more of the above can becombined for a greater influence on wateractivity


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Microbial growthDecreasing quickly with

declining aw- value

There is no more

microbial growth under

0.6 aw


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Water activity and food preservation

Bacterial growth

1.0-0.9

Yeast and mold spoilage 0.75-0.9

pH < 4.6, an Aw < 0.6

- preservation effect


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Microbial growth


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Microbial growth

Mold

Yeast

Bacteria


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Methods to preserve food

remove water (dehydration or

concentration)

convert the free water to bound water Addition of sugars, salts

freeze the food

Immobilizes the water (and lowers the Aw)


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References

http://www.vitaliskft.com/docs/vizaktivitasp

rezentacioangol.pdf

http://en.wikipedia.org/wiki/Water_activity

http://www.fda.gov/iceci/inspections/inspec

tionguides/inspectiontechnicalguides/ucm0

72916.htm
http://www.vitaliskft.com/docs/vizaktivitasprezentacioangol.pdfhttp://www.vitaliskft.com/docs/vizaktivitasprezentacioangol.pdfhttp://en.wikipedia.org/wiki/Water_activityhttp://www.fda.gov/iceci/inspections/inspectionguides/inspectiontechnicalguides/ucm072916.htmhttp://www.fda.gov/iceci/inspections/inspectionguides/inspectiontechnicalguides/ucm072916.htmhttp://www.fda.gov/iceci/inspections/inspectionguides/inspectiontechnicalguides/ucm072916.htmhttp://www.fda.gov/iceci/inspections/inspectionguides/inspectiontechnicalguides/ucm072916.htmhttp://www.fda.gov/iceci/inspections/inspectionguides/inspectiontechnicalguides/ucm072916.htmhttp://www.fda.gov/iceci/inspections/inspectionguides/inspectiontechnicalguides/ucm072916.htmhttp://en.wikipedia.org/wiki/Water_activityhttp://www.vitaliskft.com/docs/vizaktivitasprezentacioangol.pdfhttp://www.vitaliskft.com/docs/vizaktivitasprezentacioangol.pdf


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